Electron discharge device



Dec. 30, 1941- c. v. PARKER ET AL 2,268,165

' ELECTRON DISCHARGE DEVICE Filed April 4, 1940 FIG? F/G./ 7 /5b A 45 .34

L I MPAR/(ER' I}! .:i INVENTORS'ALSAMUEL- ATTORNEY Patented Dec. 30, 1941 FICE ELECTRON DISCHARGE Carlyle'V. Parker, New York, Y., and Arthur L. Samuel, Summit, N. J., assignors to Bell tTele phone Laboratories, Incorporated, New York N. Y., a corporationof New York I Application April 4, 1940, Serial No. 327,826

5 Claims. (01. 250F162 This invention relates to electron discharge devices and more particularly to electron guns for producing a. concentrated electron beam having a point focus, in cathode ray and similar electron discharge devices.

As described in the applications Serial No. 307,233, filed December 2, 1939, and Serial No. 319,393, filed February 2, 1940, of John R. Pierce, rectilinear electron motion between spaced electrodes of an electrode system or electron gunmay be achieved' by producing, in the system or gun and in the regions traversed by and outside of the electron beam, particular potential distributions such that the fieldsoutside the beam satisfy Laplaces equation and, over the boundary of the beam, are consistent with solutions of the space charge equations inside the beam, Stated in another way, the potential distribution should be such that the field outside of the beam shall match in potential the field inside the beam and shall have zerogradient normal to the boundary of thebeam. i 1 i y 1 One of the: principal problems entering into the realization of the requisite potential distribution is the determination of. the configuration and relation ef the electrodesurfaces inthe system necessaryfor effecting the desired rectilinear motion and focussi'ng oi the electrons in the beam. Inasmuch as the potential distribution along the beam boundary is a relatively complex function of distance from the electron source in the elec trode' system, the electrode configurations heretofore obtained have been relatively complex.

Onegeneral object of this invention is i to facilitate the" fabrication and construction of an electron for producing an electron beam of a desired cross sectionand focus. 1 Morespecifically, one object of this invention is to; simplify the configuration of the electrodes in an electron gun, for establishing rectilinear motion of the electrons in'the beam produced by the guns) In: one illustrative embodiment of this invention, an electron gun comprises an electron.

source, such as a cathode, and a pair of spaced centrally apertured-beam-forming electrodes in alignment with the electron source, the source and opposed surfaces of the electrodes being of such; configuration that the electrons emanating from the source are concentrated into a beam and have rectilinear motion therein. In a. specific embodiment of this invention, the source and surfaces mentioned are coaxial, symmetrical about theaxis and are of such. configuration that the electrons emanating from the source traverse rectilinear paths converging toward a point on the axis.

electrodes are [of such configuration that the generatrices. thereof consist of straight lines or straight lines and arcs of; circles.

i The invention and: the foregoing and other featuresrthereef will be; understood. more clearly and fully from'the following. detailed description with reference. to the. ac'companyingdrawing in which:

Fig. 1 is: anl'elevational view, partly in section, of: anel'ectrorr discharge device including an electrongun constructed in accordance with this invention, portionsof the electrongun being broken away; i i i Fig. 23isan enlarged. sectional view ofthe electron gun. embodied in the device. illustrated in Fig. 1;:ancl 3 Fig. .3 is. a ,top; view of apparatus, employed in determining the configuration of the electrode surfaces I'IIYthG electron gun shown; in Fig. 2.

Referring." now; .to the drawing, the electron discharge device shown in Fig. 1, which is particularly suitable for use as an amplifier at ultrahigh frequencies, for example, frequencies corresponding toi wave-lengths of the order of fifteen centimeters, comprises an elongated evacuated enclbsing vessel Ill-having; atone end thereof an inwardly extending stem H terminating in a triarmed'press and; from which an electron gun is supported.

The electron gun comprises, in general, an electro'rrsource, such, for example, as a cathode having an electron emissive surface la and a pair of beam-forming electrodes land 15 having opposedisurfaces M a, l l'b andl5'a, l-5b, respectively, of 'arc'onfiguration described in detailhereinafter. llhetelectrodesj of the gun preferably are coaxial, the axis being indicated by line A-A, and the various surfaces thereof aforenoted are symmetrical about this axis. i i i Mounted at the other end of the enclosing vessel 1.0 is an electron receiving element l6 upon whichthe electron beam produced by the electron gun impinges; This element may be a cupshaped metallic anode coaxially mounted with the electrongunand preferably is relatively deep t'orprevent the issuance of any secondary electronsproducedby impingement of the electron beam upon the inner surfaces of the anode. The electron receiving element, of course, may be of other formsi For example, it maybe a fluorescentfl screen or target. V -One or'more electrodes may be provided between the electron gun and the electron receiving a secondary electron emissive element for afiecting, e. g., modulating the in-.

tensity of, deflecting, accelerating or retarding, the electron beam. In a specific device shown in Fig. 1, a. pair of axially aligned, centrally apertured diaphragms or disc electrodes I! are pro vided opposite the electron gun and have suitable potentials applied thereto to concentrate and to accelerate the beam produced by the gun.

Equally spaced from the axis of alignment of the various electrodes are a pair of electrodes [8 which may have suitable potentials applied thereto to retard the electron beam or to modulate the velocity thereof. A second pair of centrally :apertured axially aligned electrodes |,9 ,are mounted between the electrodes l8 and electronreceiving element I6 and may have suitable potentials ape the cylindrical portion M of the first beam forming electrode, which is provided with an annular surface 24 of arcuate section overlying the edge portion of one end of the cathode.

The cathode comprises a dished end portion l3, a cylindrical portion 25 seatedupon the supporting ring and affixed thereto and to the cylindrical portion of the electrode l4, and a heater. filament encased in insulating material 21 and disposed adjacent the end wall l3 of the cathode, the surface l3a of this wall being coated with an electron emissive material. Leading-in conductors 28 for the heater filament 26 are encased, in part, by an insulating sleeve 29 and sealed in the press'l2. The filament 26 and insulation 21 therefore may be supported upon a cup-shaped closure member 30 affixed to the ey Y lindrical wall 25.

Mounted'between the supporting ring 20 and the closure member 30 are a pair of dished'metallic baffles 3| which serveto conserve the heat produced by the filament 26 and thereby insure a high cathode efficiency. The bailies may be fitted on theinsulating sleeve 29 and are spaced by a metallic annulus 32 and affixed thereto. Rigidsupports, such as wires 33, extend from the support ring 2!! and are secured to one of the bafiie members 3|, as shown.

The beam-forming electrode [4 comprises a cylindrical portion seated on and affixed to the support ring 20 and is provided with axially symmetrical surfaces Ma and Mb of a configuration described hereinafter.

The beam-forming electrode I5 is mounted in coaxial relation with the cathode l3 and electrode l4 by an annular metallic plate member 34 which is carried by a metallic cylinder 35 seated upon and affixed to the supporting ring 2|. v The'electrode gun assembly described above is supported as a unit by a plurality'of rigid metallic uprights 36 'aifixed, as by welding, to the cylinder 35 and extendinglfrom collars 31 clamped about the stem lll The paths traversed by the electrons in the electron beam and,- hence, the configuration of the beam emanating from the electron gun will be dependent upon the fields extant within the beam and the region about the beam, and these fields, in turn, are determined by the configuration and relation of the emissive surface 13a and the surfaces 14a, 14b and l5a, I5b of the electrodes l4 and I5. I I

In .an electron gun, such as shown in Fig. 2, for producing a converging electron beam, the emissive surf-ace |3a of the cathode conforms to a segment of a sphere and the surfaces [4a, l4b

: and [5a, I51) are of such configuration and rela tion that all electrons emanating from the surface l3a traverse rectilinear paths which converge toward a point on the axis AA of alignment of the electrodes of the electron gun.

In order that the desired electron motion will be realized, it is necessary that the field outside of the beam boundary correspond to an axially symmetrical solution of Laplaces equation and be such that the potential gradient normal to the beam boundary is zero, and the potential along the beam boundary varies in accordance with the solutions of the space charge equations for rectilinear motion of electrons between concentric spheres. The requisite potential variation along the beam boundary may be expressed by the relation 1 where is the potential; K is a constant and a" is a function of 1' being distance from the center of curvature ofthe emissive surface l3a of the cathode and 7'0 being the radius of curvature of this emissive surface. The constant K may be expressed by the relation i w Y K (29.34 x 10- v where 1. is the current which would flow between two concentric spheres; .The values of a for par ticular ratios of may be determined in ways known in the art.

The configurations for the surfaces l4a, I41; and Mia, l5b can be determined through the use of an electrolytic tank apparatus as described in the application Serial No. 319,393, of John R. Pierce noted hereinabove. In brief, and asillustrated in Fig. 3, such apparatus comprises a tank 40 having an inclined bottom wall of insulating material and containing an electrolyte M, such as water. The water line on the inclined bottom wall is indicated at A-A in Fig. 3 and represents or corresponds to the axis of the electron gun, A strip 42 of insulating material is mounted in the tank normal to the base and has mounted on one face thereof a plurality of conductors or probes 43. The insulating strip represents the boundary of the electron beam and is mounted so that it makes, with the axis A-A, an angle equal to the angle the elements of the conical beam boundary make with the axis of the gun. Extending from opposite ends of the insulating strip are a pair of pliant metallic strips 44 and 45.

fore, in the gun axially symmetrical fields obtain between the electrodes, the fields in any sector of the region between the electrodes will be illustrative of the fields in all other sectors.

In the electrolytic tank, it will be seen that the fields produced by potentials between the metallic strips 44 and 45 are in accordance with the Laplacian equation. Inasmuch as the strip 42 and the base wall of the tank are of insulating material, the potential gradient normal to the insulating strip and normal to the base is zero. Hence, two of the conditions requisite for the production of a converging electron beam wherein the electrons traverse rectilinear paths are established. There remains, then, only the de- 2,268,165 termination of the electrode configurations to produce the necessary variation of potential along the beam boundary, 1. e., as given by Equation 1, supra. These configurations may be established by altering the form of the metallic strips 44 and 45 until the potential along the insulating strip42, as measured at the probes or It will be appreciated that these opposed surfaces maybe of a number of configurations most ofwhich are of relatively complex form. In accordance with a feature of this invention, however, these surfaces are made of such configurations that the generatrices thereof consist of straight lines or of straight lines and arcs of circles. l

Thus, in the case of a converging electron beam, such as illustrated in Fig. 2, it has been found that the fields requisite for rectilinear electron motion may be realized if the surface I3a is a segment of a sphere, theelectro'de I4 is operated at cathode potential, the electrode 15 is operated at a positive potential with respect to the cathode and the generatrices of the surfaces Ha, Nb and [5b are straight lines and the generatrix of the surface I5a is an arc of a circle. In a specific embodiment, for which the included angle of the beam boundary is 84 degrees and the potential along the beam boundary varies in accordance with Equation 1 for a value fl: T 1.88

the surfaces I 3a and [5a ares'egments of concentric spheres, the elements of the frustoconical surface l4 a extend at an angle of 67.5 degrees to the normal :n-a: to the emissive surdescribed, it will be understood, of course, thatl it is but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims. a

What is claimed is:

1. An electron gun for electron discharge devices comprising an electron emissive surface,

and means for establishing such fields adjacent said surface that substantially all electrons emanating from said surface traverse rectilinear pathsfwithin a predetermined boundary extending from adjacent said surface, said means comprising a pair of spaced electrodes opposite and in alignment" with said surface and having op- 1.

posed axially symmetrical surfaces of revolution, the generatrix of one of said opposed surfaces including a straight line extending from adjacent the periphery of said emissive surface and awayfrom said surface and including also a second straight line extending toward and substantially normal to the axis of alignment of said electrodes from the end of said first straight line remote from said emissive surface, and the. generatrix of the other of said opposed surfaces including a straight line opposite and parallel to said second straight line and including also a second line extending toward said emissive surface from the inner end of said third straight line.

2. An electron gun for electron discharge devices comprising a concave emissive surface, and

means for establishing such fields adjacent said surface that substantially all electrons emanating from said surface traverse converging rectilinear paths within a conical boundary along which the potential varies substantially in accordance with the relation re being the radius of curvature of said emissive surface and 1 being distance from the center of curvature of said emissive surface, said means comprising a pair of spaced electrodes opposite and in alignment with said surface and having opposed axially symmetrical surfaces of revolution, the generatrix of one of said opposed surfaces consisting of straight lines and the generaa trix of the other of said opposed surfaces consisting of a straight line and an arc of a circle.

3. An electron gun for electron discharge devices comprising an electron emissive surface corresponding to a portion of a sphere, and a pair of spaced centrally apertured electrodes opposite and coaxial with said emissive surface and having opposed axially symmetrical surfaces of revolution, one of said opposed surfaces comprising a frusto-conical portion extending from immediately adjacent the periphery of said emissive surface and flaring outwardly therefrom and 5. An electron gun for electron discharge devices comprising an electron emissive surface conforming to a segment of a sphere, a centrally apertured electrode opposite said surface and coaxial therewith and having an axially symmetrical surface opposed to said emissive surface,

which includes an inner portion conforming to a segment of a sphere and concentric with said emissive surface and an *outer'annular portion extending normal to the axis of coaxiality of said surface and electrode, and a second electrode between said surfaces, coaxial therewith and having an axially symmetrical inner surface which includes a frusto-conical portion extending from immediately adjacent the periphery of said emissive surface and an annular portion extending inwardly from the end of said frusto-conical portion remote from said emissive surface, and

substantiallynormal to said axis, the elements of said frusto-conical portion being inclined outwardly with respect to said axis and at an angle of substantially 67.5 degrees to the normal to said emissive surface at the periphery thereof.

CARLYLE V. PARKER. ARTHUR L. SAMUEL. 

